Characterizing Ozone Sensitivity to Urban Greening in Los Angeles Under Current Day and Future Anthropogenic Emissions Scenarios

Abstract

Cities are simultaneously implementing urban greening and reducing anthropogenic emissions to combat climate change, but these strategies can have complex and potentially counteracting effects on regional atmospheric chemistry. Urban greening can increase emissions of volatile organic compounds (BVOCs), while climate change mitigation strategies reduce co‐emitted pollutants like nitrogen oxides (NOx). The nonlinear relationship between ozone (O3) and BVOC and NOx concentrations makes it crucial to investigate potential interactions between urban greening and anthropogenic emissions reductions. Here, we use regional atmospheric chemistry modeling to assess O3 sensitivity to a 50% increase in urban vegetation in the Los Angeles Basin. We evaluated potential interactions between urban greening and climate change mitigation by running urban greening simulations with current day and future anthropogenic emissions that reflect renewable energy adoption and electrification in Los Angeles, CA. Our model results show that urban greening increased daily maximum 8‐hour ozone concentrations, with higher increases modeled under current day anthropogenic emissions. Urban greening had complex effects on hourly O3 concentrations, with increased O3 concentrations up to 0.95 ppb during the day following increased biogenic emissions and reduced urban O3 concentrations up to 0.41 ppb at night following reduced ventilation of NOx. Under the future anthropogenic emissions scenario, reductions in NOx somewhat mitigated the daytime O3 penalties of urban greening but also dampened nighttime O3 reductions. Our results suggest that urban greening will likely have regional O3 penalties if new vegetation is high isoprene emitting, even as NOx emissions are drastically reduced following climate change mitigation.

Unheralded contributions of biogenic volatile organic compounds from urban greening to ozone pollution: a high-resolution modeling study

“…The study evaluates the effects of UGS-BVOC and UGS-LUCC on MDA8 O3 concentrations in Guangzhou, both individually and in combination. The analysis reveals that the UGS-BVOC emissions alone (Figure 6 A) primarily affect urban areas, significantly increasing MDA8 O3 concentrations by 2.2-3.0 μg/m³ (+2.3-3.2%), which increment aligns with findings from Los Angeles, where Schlaerth et al, (2023) reported a contribution of 2.5 μg/m³ from UGS-BVOC to urban MDA8 O3 levels. In contrast, the sole impact of the UGS-LUCC this change also reduces the height of the urban canopy, diminishing its shading effects on solar radiation and paradoxically leading to higher temperatures in some regions.…”

Changes in the Direct Climate Effect of Black Carbon Aerosols in East Asia Under the “Dual Carbon” Goal of China

“…The instantaneous DRF at the TOA is stronger in northern China than in the south (Figure 3), resulting from the disparity in surface albedo between the two regions (Figure S5 in Supporting Information ). The higher surface albedo in northern China compared to the south might be primarily due to larger snow cover and bare surfaces, such as the Gobi Desert (He et al., 2014; Schlaerth et al., 2023; Yan et al., 2021), especially in the winter months (Figure S5 in Supporting Information ). Surfaces with high albedo could reflect more solar radiation back to the atmosphere, enhancing the absorption of this reflected radiation by BC, which would induce a stronger positive IDRF and a weaker negative IDRF under the same aerosol loading conditions (W. Chen et al., 2021; Ocko et al., 2012; Zhuang et al., 2014).…”

Temperature-Dependent Evaporative Anthropogenic VOC Emissions Significantly Exacerbate Regional Ozone Pollution

“…Studies have shown that global warming may increase the frequency and intensities of heatwaves and urban heat island effects, , such that the impacts of temperature-dependent AVOC emissions on ozone may become more pronounced in the future. Other underestimated or unrepresented natural and anthropogenic emissions of ozone precursors, such as soil-NO x emissions and emissions associated with urban greening practices, − may also cause complex ozone-temperature sensitivities. These linkages between air pollution and meteorology should be considered in our projection of long-term air quality trends to better inform the long-term emission reduction goals.…”